Five construction workers were killed Wednesday afternoon in the outskirts of Lomanthang, the district headquarters of the remote trans-Himlayan district of Mustang bordering Tibet, in an explosion of a bomb left behind by Tibetan Khampa guerrillas nearly 25 years ago, government sources said.

The bomb exploded while workers were erecting a compound wall of a house in the outskirts of the district headquarters. A police inquiry team has been dispatched Mustang to investigate the blast as Maoist involvement has been ruled out, sources said.

Mustang was the base of Tibetan guerrillas for anti China activities from Nepal in the 1960’s and the early 1970’s.